How much CSS can the web DSL handle?

I posted a question in Libraries about CSS transitions that perhaps I should have posted here. I’m having similar issues trying to add a simple gradient background - LinearGradientStep seems to be a sealed interface, not a class with constructor parameters.

Are these things supposed to work, or does the code I see on GitHub have no connection to the libraries available in IDEA 2023.3 (Community Edition)? Fwiw, my web toy is based on the Kotlin-to-Javascript sample project, and I keep wondering if I just need to tweak project settings the right way.

After asking on the Slack channel, it turns out that in this case the linearGradient() parameter type LinearColorStop is a sort of placeholder -

                        backgroundImage = linearGradient(
                            angle = 90.deg,
                            rgba(0, 255, 0, .5),
                            rgba(2554, 255, 0, .5),
                            rgba(255, 0, 0, .5)

works just fine.